1. Field of the Invention
This invention relates generally to improvements in valves, and more particularly, but not by way of limitation, to rotary valves with spring biased valve members.
2. Description of the Prior Art
It is well known in the prior art to employ screw type needle valves between a source of high pressure fluid and a pressure gage in order to permit periodic pressure readings at the pressure gage without subjecting the pressure gage to constant application of the high pressure fluid. Such valves provide limited utility since their sealing capability degenerates rapidly when the valve is cycled between the open and closed positions.
Many of the prior art valves employed in high pressure application are constructed with bonnets threadedly secured to the valve bodies to provide a fluid-tight seal about the valve stem which is constantly loaded under pressure and maintained within the valve body by the bonnet. Such valve structures are often hazardous in high pressure corrosive environments due to the fact that often the manipulation of the valve stem in an effort to open the valve causes the bonnet, which has become corroded to the valve stem, to be disengaged from the valve body. Such loosening of the bonnet from the valve body presents an extreme hazard in high pressure and corrosive environments where the valve member, valve stem and bonnet may be blown out of the valve body in response to the high pressure applied to the valve.
The usual configuration of the prior art needle valve structures places the needle valve member downstream from the corresponding valve seat so that the pressure differential across the engaged valve member and valve seat tends to unseat the valve member from the valve seat thus promoting leakage past the valve. Once such leakage starts, it often results in the destruction of the valve seat and the ultimate destruction of the valve thereby requiring the replacement with the attendant inconvenience and expense. The use of relatively soft valve seats in prior art gage valves and the like to increase the sealing engagement between the valve member and valve seat is accompanied by a reduction in the maximum fluid pressure the valves can handle.